1. Field of the Invention
The invention relates to display devices. More specifically, the invention describes a method and apparatus capable of providing a robust encryption of a audio/video data in a packet based transmission environment.
2. Overview
Protection of proprietary digital content has become an important consideration and more particularly, in high definition (HD), high-bandwidth applications. Especially important for HD, high-bandwidth applications, content protection provides assurances that owners of digitized content are protected from unauthorized use and copying of their proprietary content. A popular high-bandwidth digital-content protection scheme developed by Intel Corporation of Santa Clara Calif. commonly referred to as HDCP has been widely implemented. As currently configured, this particular HDCP protocol is specifically designed for use in Digital Visual Interface (DVI) and High-Definition Multimedia Interface (HDMI) based environments.
In general, HDCP encrypts the transmission of digital content between the video source, or transmitter—such as a PC, DVD player or set-top box—and the digital display, or receiver—such as a monitor, television or projector. In this way, HDCP is designed to prevent copying or recording of digital content thereby protecting the integrity of content as it is being transmitted. For example, as required by the described HDCP protocol, during an authentication phase, the receiver will only be provided with content once it demonstrates knowledge of the authentication keys which the transceiver verifies through computation of a secret value. Furthermore, to prevent eavesdropping and stealing of the data, the transmitter and receiver will generate a shared secret value that is consistently checked throughout the transmission. Once authentication is established, the transmitter encrypts the data and sends it to the receiver for decryption.
The current implementation of the DVI standard requires the use of a set of defined characters based upon a 10 bit transmission protocol. For example, as currently configured, only 460 characters (out of a possible 1024 available) are used by the receiver for data while 4 characters are used as explicit control signals such as hsync and vsync. In this arrangement, any time the receiver receives and recognizes one of the predefined characters representing data, then the received implicitly defines a data enable signal (DE) as being active thereby indicating that the received data is true data. However, whenever one of the 4 control characters is received by the receiver, then an implicit assumption is made that data enable (DE) is inactive.
HDCP protocol uses the status of DE, Hsync, Vsync and another control signal, called CNTL3, to advance its state machine. The DE, Hsync, and Vsync signals are timing signals associated with raster video transmitted in a “streaming” manner. In a streaming transfer, the pixel data is transferred at pixel rate and the ratio of blanking period to data period is preserved. In case of a packet transfer, these timing signals may not be present. Only the pixel data may be transferred in the packet stream, while timing information is communicated in a different way.
It would be advantageous from a commercial cost standpoint to be able to support HDCP protocol over cheaper type cables such as coax cable, cat 5 cable, and so on. Unfortunately, however, in order to properly implement the HDCP protocol, a sideband handshake is required in order to at least synchronize the source and the sink devices which in conventional arrangements would require at least two separate data lines. In this way, coax cable, cat 5 cable and the like is unsuitable for implementing the HDCP protocol in a conventional manner.
Therefore, what is required is a way to support high-definition copy protection that is compatible with existing high definition copy protection protocols such as HDCP over single cable, such as coax cable.